Electrical calculator

Two worked examples, start to finish

The fastest way to trust a formula is to walk through it. Example one, a car headlamp: a 12 V bulb rated at 60 W. Current is power divided by voltage — 60 ÷ 12 = 5 amps — and resistance follows from Ohm's law: 12 ÷ 5 = 2.4 ohms. Example two, a kettle on European mains: 230 V and 2000 W. Current is 2000 ÷ 230, about 8.7 A, and the element's working resistance is 230 ÷ 8.7, about 26.5 ohms. Notice what happened both times: knowing any two of the four values pinned down the other two. That is the whole idea of the calculator — pick the pair you have from the I know list, and the remaining pair follows with no algebra on your side.

What changes with AC: RMS and power factor

Mains electricity alternates, and the 230 V on your wall is already an RMS figure — a kind of honest average, defined precisely so that the familiar formulas keep working. For purely resistive loads — heaters, kettles, toasters, old-fashioned bulbs — you can therefore use this calculator on mains exactly as on a battery. The complication arrives with motors, compressors and electronics: their current runs partly out of step with the voltage, so volts times amps gives the apparent power in VA, of which only a fraction — the power factor — is real power doing work. A motor drawing 4 A at 230 V is pulling 920 VA but may be delivering closer to 700 W. For such loads, read the calculated wattage as a ceiling rather than a promise.

Volts, joules, and the water analogy

The question that brings many people to this page is some form of how many joules is 230 volts — and the honest answer is that the question is incomplete, like asking how far 50 km/h is. The water analogy makes it click: voltage is the pressure in the pipe, current is how much water is flowing, power is how hard the stream is working right now, and energy is the total water delivered by the end. Pressure alone fills no bucket. A concrete run through the energy calculator: a 2 kW heater running for 3 hours uses 2 × 3 = 6 kWh — which is 21.6 million joules, and the 6 kWh figure is the one your electricity meter records. The 230 V never entered that sum directly; it only mattered because the heater drew its current at that voltage.

What this calculator must not be used for

A number that is correct on paper can still be unsafe in a wall. Do not use these results to size cables, fuses or circuit breakers: real installations involve derating for cable length, bundling and insulation, inrush currents that briefly run several times the steady figure, and local wiring regulations — that is an electrician's territory, and mains voltage has earned the respect. Use the calculator for what it is genuinely good at: sanity-checking a device's current draw, decoding a rating plate, sizing a resistor in a low-voltage hobby circuit, or estimating running costs. For that last one, a tip: once you have an energy figure, our free Unit converter has an energy category that flips it between joules, watt-hours, kilowatt-hours, calories and BTU — any direction, instantly.

Why you can't convert volts to joules

Volts and joules measure different things, so there is no fixed "1 V = X J" factor. Voltage (volts) is electrical pressure, current (amps) is how much charge flows, power (watts) is how fast energy is delivered, and energy (joules) is the total amount delivered. They connect only through the real formulas: power = voltage × current (P = V × I), and energy = power × time (E = P × t). A 230 V outlet by itself tells you nothing about energy until something draws current through it for some amount of time.